How to not break themes

Themes allows users to load custom CSS and .ui files. The latter means that tinkering with the .ui files can cause themes to break. Here's some hints what to watch out for.

Promoting widgets

Any widget you promote won't be promoted in the theme for the previous version, so you'll have a base class instead of a subclass. If you use some functions of the subclass that aren't there in the base class, things will break. Try to avoid promoting if you can put the functionality you need in a separate class instead of a subclass.

Signals and slots

Changing existing widgets' signals and slots that are used in the logic will break themes. If you need to change them, let the themers know.